The demand for finding and exploiting sources of petroleum beyond those currently known and used has often required the drilling of oil wells in remote places. Once a well has been drilled, the pumping unit must be assembled and erected over the well head so that the oil can be pumped out of the well. When the well has been exhausted, which could happen after a relatively short time, or if the well is unproductive, the pumping unit must be disconnected, taken down and moved to a new well site. Therefore, efficient exploitation of these wells requires petroleum pumping units which may be easily transported, often over rough terrain, to the oil field and quickly erected over the well head without a large work crew. Additionally, an ideal unit for use under such conditions must be easily taken down, moved to a new well head site and re-erected with a minimal expenditure of time.
An ideal pumping unit must be versatile as well as easily transportable and erectable. Once a petroleum pumping unit is in place over the well head, conditions affecting the pumping operations will arise. For example, the viscosity of the oil may vary considerably from well to well or may even exhibit variation during pumping operations in a single well. As oil viscosity increases, resistance to pumping increases and the equipment is subjected to greater stress. Pumping equipment must be able to respond effectively and efficiently to such variations in oil viscosity if maximum exploitation of a well is to be achieved. In particular, excessive stress and strain on the well polish rod must be minimized, regardless of oil viscosity or other variable conditions encountered at a well site. In a remote oil field, a substantial period of time can be lost if a broken or bent polish rod has to be replaced.
Conventional oil well pumps of the walking beam of "horse head" type, like those disclosed in U.S. Pat. No. 3,513,387 to Sadouet, include many bulky, heavy parts which are difficult to transport and even more difficult to assemble and disassemble rapidly at the well head under conditions typically found in remote oil fields. Additionally, the stroke of these "horse head" pumps is limited by the length of the walking beam. An increase in the length of stroke is achieved by providing a single vertical mast which may be collapsible to facilitate shipment to the field, as disclosed in U.S. Pat. Nos. 3,535,985 to Attebo; 3,777,491 to Bender; 3,782,117 to James and 4,114,735 to Saruwautari. While the units disclosed in the aforementioned patents provide a longer stroke, are easier to ship and, in the case of the unit disclosed by Saruwautari, are easier to erect than the walking beam type pumps, these collapsible pumping units do not incorporate the versatility necessary to compensate for many variations in pumping conditions, such as oil viscosity variations. Additionally, in single mast units, the hydraulic cylinder and piston to operate the pump are located directly over the polish rod in axial alignment therewith, making it impossible to rapidly connect the pumping unit to polish rods which project at different heights above the well head. Furthermore, these single mast units are not always as stable as desired once they have been installed.
Pumping units known to the prior art which include structure to minimize strain on the well polish rod are disclosed in U.S. Pat. Nos. 1,845,176 to Palm, 2,073,809 to Salentine, 2,683,424 to Kane, and 3,153,387 to Sadouet. Most of these units employ a system of counterweights to assist in powering a single hydraulic cylinder during the up stroke to raise the polish rod. Counterbalancing the hydraulic cylinder effectively assists in raising the polish rod through viscous oil without rod damage. However, no simple means to easily change the counterweights on a hydraulic pumping unit are disclosed by the prior art.
Consequently, a need exists for a portable petroleum pumping unit which may be easily shipped and transported to remote oil fields, readily and quickly erected at the well head by a minimal work crew to form a very stable supporting structure for the pumping apparatus, and which includes features whereby the unit may be readily adapted to compensate for variations in pumping conditions and still function at optimum efficiency.